Method of fabricating a light emitting device

ABSTRACT

There is provided an inexpensive light emitting device and an electronic instrument using the same. In this invention, photolithography steps relating to manufacture of a transistor are reduced, so that the yield of the light emitting device is improved and the manufacturing period thereof is shortened. A feature is that a gate electrode is formed of conductive films of plural layers, and by using the selection ratio of those at the time of etching, the concentration of an impurity region formed in an active layer is adjusted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device (hereinafter referred to as alight emitting device) including an element (hereinafter referred to asa light emitting element) having a luminous material interposed betweenelectrodes. Particularly, the present invention relates to a lightemitting device including a light emitting element (hereinafter referredto as an EL element) using, as a luminous material, an organic compoundin which EL (Electro Luminescence) is obtained. Incidentally, an organicEL display and an organic light emitting diode (OLED: Organic LightEmitting Diode) are included in the light emitting device of the presentinvention.

The luminous material which can be used for the present inventionincludes any luminous materials which emit light (phosphorescence and/orfluorescence) through singlet excitation, triplet excitation, or bothexcitations.

2. Description of the Related Art

In recent years, research of an EL element has proceeded in which a thinfilm capable of obtaining EL and made of an organic compound isinterposed between an anode and a cathode, and development of a lightemitting device using self luminescence of the EL element has proceeded.In the development of this light emitting device, although a passivematrix type has been the mainstream, there is a fear that when a pixelportion becomes highly fine, the light emitting brightness of the ELelement must be increased, so that the reliability (the long life of theEL element) can not be secured.

Then, recently, attention has been paid to an active matrix type inorder to attain a highly fine display. The active matrix type lightemitting device has a feature that an input signal is controlled by asemiconductor element provided in each pixel to make an EL element emitlight, and a transistor is generally used as the semiconductor element.

A typical pixel structure is such that two transistors are included in apixel and have different roles respectively, and the light emittingbrightness of the EL element can be controlled. As a result, a lightemitting period is almost equivalent to one frame period, and even if apixel portion becomes highly fine, it becomes possible to display animage while the light emitting brightness is suppressed. Thus, it hasbeen considered that the active matrix type is effective for a lightemitting device including a highly fine pixel portion.

However, in the active matrix type light emitting device, a plurality oftransistors are formed on the same substrate, and it is difficult toensure the yield as compared with a passive matrix type of a simplestructure. Besides, since a manufacturing process of a transistor isrelatively complicated, there is a fear that the manufacturing costbecomes high as compared with the passive matrix type light emittingdevice. Further, in that case, there is a fear that the unit cost of anelectric instrument using the active matrix type light emitting deviceas its display portion is also raised.

SUMMARY OF THE INVENTION

The present invention has an object to provide a technique forfabricating an active matrix type light emitting device having a lowmanufacturing cost. This object is especially pursued in the lightemitting device having a number of photolithography steps as comparedwith an active matrix type liquid crystal display device.

Further, the present invention has another object to decrease themanufacturing cost of an electric instrument using the active matrixtype light emitting device as a display portion.

According to the present invention, photolithography steps relating tomanufacture of a transistor are reduced, so that the yield of a lightemitting device is improved, the manufacturing period is shortened, andthe manufacturing cost is reduced. The feature is that a gate electrodeis formed of a plurality of conductive films, and the selection ratio ofthose at the time of etching is used to make a highly reliablestructure. Incidentally, in the present specification, a transistorincludes a MOS transistor and a thin film transistor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F are views showing manufacturing steps of an n-channeltransistor.

FIGS. 2A to 2E are views showing manufacturing steps of a light emittingdevice.

FIGS. 3A to 3D are views showing manufacturing steps of the lightemitting device.

FIGS. 4A and 4B are views showing manufacturing steps of the lightemitting device.

FIGS. 5A and 5B are views showing an upper structure and a crosssectional structure of a light emitting device.

FIGS. 6A to 6D are views showing manufacturing steps of a light emittingdevice.

FIGS. 7A to 7C are views showing manufacturing steps of a light emittingdevice.

FIGS. 8A to 8E are views showing manufacturing steps of a light emittingdevice.

FIG. 9 is a view showing a manufacturing step of a light emittingdevice.

FIG. 10 is a view showing a cross sectional structure of a lightemitting device.

FIGS. 11A and 11B are views each showing a circuit structure of a pixelof a light emitting device.

FIG. 12 is a view showing a cross sectional structure of a lightemitting device.

FIG. 13 is a view showing a circuit structure of a pixel of a lightemitting device.

FIG. 14 is a view showing a cross sectional structure of a lightemitting device.

FIGS. 15A to 15C are views showing manufacturing steps of a lightemitting device.

FIG. 16 is a view showing a circuit structure of a pixel of a lightemitting device.

FIGS. 17A and 17B are views each showing a structure of a light emittingdevice having an external driving circuit.

FIGS. 18A and 18B are views each showing a structure of a light emittingdevice having an external controller.

FIGS. 19A to 19F are views showing specific examples of electricinstruments.

FIGS. 20A and 20B are views showing specific examples of electricinstruments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An example of fabricating steps of an n-channel transistorcharacterizing the present invention will be described with reference toFIGS. 1A to 1F. In FIG. 1A, reference numeral 100 designates aninsulator which is a substrate provided with an insulating film on itssurface, an insulating substrate, or an insulating film. A semiconductorfilm (typically, a silicon film) 101 is formed on the insulator 100, andthis semiconductor film 101 becomes an active layer of a transistor. Thesemiconductor film 101 is covered with an insulating film 102 containingsilicon, and this insulating film 102 becomes a gate insulating film ofthe transistor. As the insulating film containing silicon, it ispossible to use a silicon oxide film, a silicon nitride film, a siliconnitride oxide film, or a laminate film of a combination of these.

Next, a conductive film in which at least two conductive films arelaminated, is formed on the insulating film 102 containing silicon.Here, a first conductive film 103 and a second conductive film 104 areformed. Here, it is preferable to make such a combination that theselection ratio at the time of etching can be secured between the firstconductive film 103 and the second conductive film 104.

As a typical example of such a combination, it is possible toenumerate 1) combination of a tantalum nitride film as the firstconductive film and a tungsten film as the second conductive film, 2)combination of a tungsten film as the first conductive film and analuminum alloy film as the second conductive film, and 3) combination ofa titanium nitride film as the first conductive film and a tungsten filmas the second conductive film.

In the combination 1), the tungsten film and the tantalum nitride filmare etched by a combination of chlorine (Cl₂) gas and a carbontetrafluoride (CF₄) gas, and an etching rate of the tantalum nitridefilm is extremely lowered by adding an oxygen (O₂) gas to this gassystem, so that the selection ratio can be secured.

In the combination 2), although the aluminum film is etched by acombination of a bromine trichloride (BCl₃) gas and a chlorine (Cl₂)gas, the tungsten film is not etched. Besides, although the tungstenfilm is etched by a combination of a chlorine (Cl₂) gas and a carbontetrafluoride (CF₄) gas, the aluminum film is not etched. In this way,the selection ratio of both can be secured.

In the case where the aluminum alloy film is used as the secondconductive film, it is preferable to provide a titanium film or atitanium nitride film as a third conductive film thereon. By doing so,contact resistance to another wiring line can be lowered, and further,there is also obtained such a merit that hillocks generated in aluminumalloy can be suppressed.

Next, as shown in FIG. 1B, the second conductive film 104 is etched byusing a resist 105, and an electrode 106 made of the second conductivefilm is formed. As an etching condition, it is preferable to perform adry etching using ICP (Inductively Coupled Plasma). As an etching gas, amixture gas of a carbon tetrafluoride (CF₄) gas, a chlorine (Cl₂) gasand an oxygen (O₂) gas is used.

As a typical etching condition, a gas pressure is made 1 Pa, and in thisstate, RF electric power (13.56 MHz) of 500 W is applied to a coil typeelectrode to produce plasma. Besides, RF electric power (13.56 MHz) of150 W is applied as a self bias voltage to a stage on which thesubstrate is put, so that a negative self bias is applied to thesubstrate. At this time, it is appropriate that the amount of the flowof the respective gases is made such that the carbon tetrafluoride gashas a flow of 2.5×10⁻⁵ m³/min, the chlorine gas has a flow of 2.5×10⁻⁵m³/min, and the oxygen gas has a flow of 1.0×10⁻⁵ m³/min. The etchingrate of the tantalum nitride film is suppressed by the existence ofoxygen.

In this state, an impurity element (hereinafter referred to as an n-typeimpurity element) for making a semiconductor an n-type semiconductor isadded to the semiconductor film 101. At this time, since the gateinsulating film 102 is covered with the first conductive film 103, theelectrode 106 made of the second conductive film is used as a mask, andthe n-type impurity element is made to pass through the first conductivefilm 103 and is added. That is, the n-type impurity element is added tothe semiconductor film 101 by self-alignment using the electrode 106made of the second conductive film. Specifically, an element (typically,phosphorus or arsenic) belonging to group 15 of the periodic table canbe used as the n-type impurity element.

At this time, a well-known plasma doping method or ion implantationmethod may be used as an adding method. The concentration of the elementadded in the semiconductor film may be made 1×10²⁰ to 1×10²¹ atoms/cm³.Regions 107 and 108 in which the n-type impurity element of theconcentration like this is added are called n-type impurity regions (a)in the present specification.

Next, as shown in FIG. 1C, the first conductive film 103 is etched byself-alignment using the electrode 106 made of the second conductivefilm as a mask. By this, an electrode 109 made of the first conductivefilm is formed under the electrode 106 made of the second conductivefilm.

This etching is performed by a dry etching method using the ICP, and amixture gas of a carbon tetrafluoride (CF₄) gas and a chlorine (Cl₂) gasis used as an etching gas. A typical etching condition is such that agas pressure is made 1 Pa, and RF electric power (13.56 MHz) of 500 W isapplied to a coil type electrode to produce plasma in this state.Besides, RF electric power (13.56 MHz) of 20 W is applied as a self biasvoltage to the stage on which the substrate is put, so that a negativeself bias is applied to the substrate. At this time, it is appropriatethat the flow of the respective gases is made such that the carbontetrafluoride gas has a flow of 3.0×10⁻⁵ m³/min, and the chlorine gashas a flow of 3.0×10⁻⁵ m³/min.

Next, as shown in FIG. 1D, the line width of the electrode 106 made ofthe second conductive film is narrowed by etching, and a second gateelectrode 110 is formed. The second gate electrode 110 indicates anelectrode made of the second conductive film and functioning as the gateelectrode of a transistor.

This etching is performed by a dry etching method using the ICP, and amixture gas of a carbon tetrafluoride (CF₄) gas, a chlorine (Cl₂) gasand an oxygen (O₂) gas is used as an etching gas. A typical etchingcondition is such that a gas pressure is made 1 Pa, and in this state,RF electric power (13.56 MHz) of 500 W is applied to a coil typeelectrode to produce plasma. Besides, RF electric power (13.56 MHz) of20 W is applied as a self bias voltage to the stage on which thesubstrate is put, so that a negative self bias is applied to thesubstrate. At this time, it is appropriate that the amount of the flowof the respective gases is made such that the carbon tetrafluoride gashas a flow of 2.5×10⁻⁵ m³/min, the chlorine gas has a flow of 2.5×10⁻⁵m³/min, and the oxygen gas has a flow of 1.0×10⁻⁵ m³/min. The etchingrate of the tantalum nitride film is suppressed by the existence ofoxygen.

Next, an adding step of the n-type impurity element is again carriedout. At this time, in regions designated by reference numerals 111 and112, regions are formed in which the n-type impurity element having aconcentration of 1×10¹⁷ to 1×10¹⁹ atoms/cm³ is added. The regions 111and 112 in which the n-type impurity element of the concentration likethis is added, are called n-type impurity regions (b) in the presentspecification.

In this adding step, a portion where the conductive films of at leasttwo layers are laminated, that is, a laminate portion of the electrode109 made of the first conductive film and the second gate electrode 110becomes a mask, and the n-type impurity element is made to pass througha portion where only the electrode 109 made of the first conductive filmis exposed and is added. That is, the n-type impurity element is addedto the semiconductor film 101 by self-alignment using the second gateelectrode 110.

A region 113 where the n-type impurity element is not added is a regionfunctioning as a channel formation region of the transistor, and isformed just under the second gate electrode 110.

Next, as shown in FIG. 1E, the line width of the electrode 109 made ofthe first conductive film is narrowed by etching, and a first gateelectrode 114 is formed. Note that, the first gate electrode 114indicates an electrode made of the first conductive film and functioningas the gate electrode of a transistor.

This etching is performed by a dry etching method using the ICP or a dryetching method with an RIE (Reactive Ion Etching) mode, and a mixturegas of a carbon tetrafluoride (CF₄) gas and a chlorine (Cl₂) gas is usedas an etching gas. A typical etching condition is such that a gaspressure is made 1 Pa, and RF electric power (13.56 MHz) of 500 W isapplied to a coil type electrode to produce plasma in this state.Besides. RF electric power (13.56 MHz) of 20 W is applied as a self biasvoltage to the stage on which the substrate is put, so that a negativeself bias is applied to the substrate. At this time, it is appropriatethat the amount of the flow of the respective gases is made such thatthe carbon tetrafluoride gas has a flow of 2.5×10⁻⁵ m³/min, the chlorinegas has a flow of 2.5×10⁻⁵ m³/min, and the oxygen gas has a flow of1.0×10⁻⁵ m³/min.

Note that, although this etching step has an object to etch theelectrode 109 made of the first conductive film (tantalum nitride film),the etching rate of the tantalum nitride film is suppressed by addingthe oxygen gas. This is for achieving fine adjustment of the etchingamount of the electrode 109 made of the first conductive film.

At this time, a feature is that etching is stopped at a place where anend portion of the first gate electrode 114 overlaps a part of each ofthe n-type impurity regions (b) 111 and 112 through the gate insulatingfilm 102. That is, the n-type impurity region (b) 111 is divided into aregion 111 a not overlapping the first gate electrode 114 and a region111 b overlapping there through the gate insulating film 102. The n-typeimpurity region (b) 112 is also divided into a region 112 a notoverlapping the first gate electrode 114 and a region 112 b overlappingthere through the gate insulating film 102.

Thereafter, as shown in FIG. IF, when a passivation film 116, aninterlayer insulating film 117, a source wiring line 118 being incontact with the semiconductor film which becomes the active layer ofthe transistor, and a drain wiring line 119 are formed, the n-channeltransistor is completed. As the passivation film 116, a silicon nitridefilm or a silicon nitride oxide film may be used. As the interlayerinsulating film 117, an inorganic insulating film, an organic insulatingfilm, or a laminate film of those may be used. As the organic insulatingfilm, a resin film of polyimide, acryl resin, polyamide, or BCB(benzocyclobutene) may be used. Besides, a well-known conductive filmmay be used as the source wiring line 118 and the drain wiring line 119.

In the above fabricating steps, photolithography steps are carried outfor four times, that is, at the time of formation of the semiconductorfilm 101, at the time of formation of the electrode 106 made of thesecond conductive film, at the time of formation of contact holes of theinterlayer insulating film 117, and at the time of formation of thesource wiring line 118 and the drain wiring line 119. In the case wherea CMOS circuit is formed, although the photolithography steps areincreased by one in order to fabricate a p-channel transistor, the stepsare carried out only for five times nevertheless.

In the transistor of FIG. 1F, the n-type impurity region (b) 112 isformed between the channel formation region 113 and the drain region108. Here, in the n-type impurity region (b) 112, the region designatedby reference numeral 112 b overlaps the first gate electrode 114 throughthe gate insulating film 102, and this structure is very effective toprevent hot carrier deterioration. Besides, in the n-type impurityregion (b) 112, the region designated by the reference numeral 112 a isa region having the same function as a conventional LDD (Lightly DopedDrain) region.

Accordingly, in the transistor of FIG. 1F, a hot carrier countermeasureis taken by the region 111 b or 112 b, and a leak current countermeasureis taken by the region 111 a or 112 a, so that a highly reliablestructure is made. Like this, since the highly reliable transistor canbe fabricated through the five photolithography steps, not only theimprovement of the yield of the light emitting device including thelight emitting element and the shortening of the manufacturing periodare realized, but also the inexpensive and highly reliable lightemitting device can be fabricated.

Hereinafter, embodiment mode of the present invention will be describedin detail using the embodiments described below.

Embodiment 1

In this embodiment, a description will be given of a method ofmanufacturing a pixel portion and a driving circuit provided at itsperiphery on the same insulator. However, for simplification of thedescription, with respect to the driving circuit, a CMOS circuit inwhich an n-channel transistor and a p-channel transistor are combinedwill be shown.

First, as shown in FIG. 2A, a glass substrate 201 is prepared. In thisembodiment, not-shown protection films (carbon films, specificallydiamond-like carbon films) are provided on both surfaces (the frontsurface and the rear surface) of the glass substrate 201. As long as itis transparent to visible light, a material other than glass (forexample, plastic) may be used.

Next, an under film 202 having a thickness of 300 nm is formed on theglass substrate 201. In this embodiment, as the under film 202, siliconnitride oxide films are laminated and are used. At this time, it isappropriate that the concentration of nitrogen of a layer adjacent tothe glass substrate 201 is made 10 to 25 wt %, and nitrogen is made tobe contained at the concentration rather higher than that of anotherlayer.

Next, an amorphous silicon film (not shown) having a thickness of 50 nmis formed on the under film 202 by a sputtering method. Note that, it isnot necessary to limit the film to the amorphous silicon film, but anysemiconductor films (including a microcrystalline semiconductor film)containing amorphous structure may be used. As the amorphoussemiconductor film, an amorphous silicon film or an amorphous silicongermanium film (a silicon film containing Germanium at a concentrationof 1×10¹⁸ to 1×10²¹ atoms/cm³) may be used. The film thickness may be 20to 100 nm.

Then, crystallization of the amorphous silicon film is performed byusing a well-known laser crystallizing method, and a crystalline siliconfilm 203 is formed. In this embodiment, although a solid laser(specifically, second harmonic of Nd:YAG laser) is used, an excimerlaser may also be used. As the crystallizing method, a furnace annealingmethod may be used.

Next, as shown in FIG. 2B, the crystalline silicon film 203 is etched bya first photolithography step to form island-like crystalline siliconfilms 204 to 207. These are crystalline silicon films which subsequentlybecome the active layers of transistors.

Note that, in this embodiment, although the crystalline silicon filmsare used as the active layers of the transistors, an amorphous siliconfilm can also be used as the active layer.

Here, in this embodiment, a protection film (not shown) made of asilicon oxide film and having a thickness of 130 nm is formed on theisland-like crystalline silicon films 204 to 207 by a sputtering method,and an impurity element (hereinafter referred to as a p-type impurityelement) to make a semiconductor a p-type semiconductor is added to theisland-like crystalline silicon films 204 to 207. As the p-type impurityelement, an element (typically, boron or gallium) belonging to group 13of the periodic table can be used. Note that, this protection film isprovided to prevent the crystalline silicon film from directly beingexposed to plasma when the impurity is added, and to enable fineconcentration control.

The concentration of the p-type impurity element added at this time maybe made 1×10¹⁵ to 5×10¹⁷ atoms/cm³ (typically, 1×10¹⁶ to 1×10¹⁷atoms/cm³). The p-type impurity element added at this concentration isused to adjust the threshold voltage of the n-channel transistor.

Next, the surfaces of the island-like crystalline silicon films 204 to207 are washed. First, the surface is washed by using pure watercontaining ozone. At that time, since a thin oxide film is formed on thesurface, the thin oxide film is removed by using a hydrofluoric acidsolution diluted to 1%. By this treatment, contaminants adhered to thesurfaces of the island-like crystalline silicon films 204 to 207 can beremoved. At this time, it is preferable that the concentration of ozoneis 6 mg/L or more. The series of treatments are carried out withoutopening to the air.

Then, a gate insulating film 208 is formed to cover the island-likecrystalline silicon films 204 to 207. As the gate insulating film 208,an insulating film having a thickness of 10 to 150 nm, preferably 50 to100 nm and containing silicon may be used. This may have a single-layerstructure or a laminate structure. In this embodiment, a silicon nitrideoxide film having a thickness of 80 nm is used.

In this embodiment, the steps from the surface washing of theisland-like crystalline silicon films 204 to 207 to the formation of thegate insulating film 208 are carried out without opening to the air, sothat contaminants and interface levels on the interface between thesemiconductor film and the gate insulating film are lowered. In thiscase, a device of a multi-chamber system (or an inline system) includingat least a washing chamber and a sputtering chamber may be used.

Next, a tantalum nitride film having a thickness of 30 nm is formed as afirst conductive film 209, and, further, a tungsten film having athickness of 370 nm is formed as a second conductive film 210. Inaddition, a combination of a tungsten film as the first conductive filmand an aluminum alloy film as the second conductive film, or acombination of a titanium film as the first conductive film and atungsten film as the second conductive film may be used.

These metal films may be formed by a sputtering method. When an inertgas such as Xe or Ne is added as a sputtering gas, film peeling due tostress can be prevented. When the purity of a tungsten target is made99.9999%, a low resistance tungsten film having a resistivity of 20 mΩcmor less can be formed.

Besides, the steps from the surface washing of the semiconductors 204 to207 to the formation of the second conductive film 210 can also becarried out without opening to the air. In this case, a device of amulti-chamber system (or an inline system) including at least a washingchamber, a sputtering chamber for forming an insulating film, and asputtering chamber for forming a conductive film may be used.

Next, resists 211 a to 211 e are formed, and the second conductive film210 is etched. As an etching condition here, the condition explained inFIG. 1B may be adopted (FIG. 2C).

By this, the second conductive film (tungsten film) 210 is selectivelyetched, and electrodes 212 to 216 made of the first conductive film areformed. The reason why the second conductive film 210 is selectivelyetched is that the progress of etching of the first conductive film(tantalum nitride film) becomes extremely slow by addition of oxygen tothe etching gas.

Note that, here, there is a reason why the first conductive film 209 ismade to remain. Although the first conductive film can also be etched atthis time, if the first conductive film is etched, the gate insulatingfilm 208 is also etched in the same step and the film thickness isdecreased. At this time, if the thickness of the gate insulating film208 is 100 nm or more, there is no problem. However, if the thickness isless than that, a part of the gate insulating film 208 is removed in asubsequent step and the semiconductor film thereunder is exposed, andthere is a possibility that the semiconductor film which becomes asource region or a drain region of a transistor is also removed.

However, the foregoing problem can be solved by leaving the firstconductive film 209 as in this embodiment.

Next, an n-type impurity element (in this embodiment, phosphorus) isadded in a self-aligning manner by using the resists 211 a to 211 e andthe electrodes 212 to 216. At this time, phosphorus passes through thefirst conductive film 209 and is added. Impurity regions 217 to 225formed in this way contain the n-type impurity element at aconcentration of 1×10²⁰ to 1×10²¹ atoms/cm³ (typically, 2×10²⁰ to 5×10²¹atoms/cm³).

Next, the first conductive film 209 is etched by using the resists 211 ato 211 e as masks. As an etching condition here, the condition explainedin FIG. 1C may be adopted. In this way, electrodes 226 to 230 made ofthe first conductive film are formed (FIG. 2D).

Next, as shown in FIG. 2E, the electrodes 212 to 216 made of the secondconductive film are selectively etched by using the resists 211 a to 211e as they are. As an etching condition here, the condition explained inFIG. 1D may be adopted. In this way, second gate electrodes 231 to 235are formed.

Next, an n-type impurity element (in this embodiment, phosphorus) isadded. In this step, the second gate electrodes 231 to 235 function asmasks, and phosphorus passes through part of the electrodes 226 to 230made of the first conductive film and is added, and n-type impurityregions 236 to 245 containing phosphorus at a concentration of 2×10¹⁶ to5×10¹⁹ atoms/cm³ (typically, 5×10¹⁷ to 5×10¹⁸ atoms/cm³) are formed.

Besides, as an addition condition here, an acceleration voltage is setquite high as 70 to 120 kV (in this embodiment, 90 kV) so thatphosphorus passes through the first conductive film and the gateinsulating film and reaches the island-like crystalline silicon films.

Next, as shown in FIG. 3A, the electrodes 226 to 230 made of the firstconductive film are etched to form first gate electrodes 246 to 250. Asan etching condition here, the condition explained in FIG. 1E may beadopted.

At this time, the first gate electrodes 246 to 250 are etched so thatthey partially overlap the n-type impurity regions (b) 236 to 245through the gate insulating film 208. For example, the n-type impurityregion (b) 236 is divided into a region 236 a not overlapping the firstgate electrode 246 and a region 236 b overlapping there through the gateinsulating film 208. The n-type impurity region (b) 237 is divided intoa region 237 a not overlapping the first gate electrode 246 and a region237 b overlapping there through the gate insulating film 208.

Next, resists 251 a and 251 b are formed, and an impurity element(hereinafter referred to as a p-type impurity element) to make asemiconductor a p-type semiconductor is added. As the p-type impurityelement, an element (typically, boron) belonging to group 13 of theperiodic table may be added. Here, an acceleration voltage is set sothat boron passes through the first gate electrodes 247 and 250 and thegate insulating film 208, and reaches the semiconductor film. In thisway, p-type impurity regions 252 to 255 are formed (FIG. 3B).

Next, as shown in FIG. 3C, as a first inorganic insulating film 256, asilicon nitride film or silicon nitride oxide film having a thickness of30 to 100 nm is formed. Thereafter, the added n-type, impurity elementand p-type impurity element are activated. As an activation means, afurnace annealing, a laser annealing, a lamp annealing, or a combinationof those can be used.

Next, as shown in FIG. 3D, a second inorganic insulating film 257 madeof a silicon nitride film or a silicon nitride oxide film is formed to athickness of 50 to 200 nm. After the second inorganic insulating film257 is formed, a heat treatment in the temperature range of 350 to 450°C. is carried out. Note that, it is effective to carry out a plasmatreatment using a hydrogen (H₂) gas or an ammonia (NH₃) gas before thesecond inorganic insulating film 257 is formed.

Next, as an organic insulating film 258, a resin film transparent tovisible light is formed to a thickness of 1 to 2 μm. As the resin film,a polyimide film, a polyamide film, an acryl resin film, or a BCB(benzocyclobutene) film may be used. Besides, a photosensitive resinfilm can also be used.

Note that, in this embodiment, the laminate film of the first inorganicinsulating film 256, the second inorganic insulating film 257, and theorganic insulating film 258 is generically called an interlayerinsulating film.

Next, as shown in FIG. 4A, a pixel electrode (anode) 259 made of anoxide conductive film which has a large work function and is transparentto visible light is formed to a thickness of 80 to 120 nm on the organicinsulating film 258. In this embodiment, an oxide conductive film inwhich gallium oxide is added to zinc oxide is formed. Besides, asanother oxide conductive film, it is also possible to use an oxideconductive film made of indium oxide, zinc oxide, tin oxide, or acompound of combination of those.

Note that, after the oxide conductive film is formed, althoughpatterning is carried out to form the pixel electrode 259, a flatteningtreatment of the surface of the oxide conductive film can also becarried out before the patterning. The flattening treatment may be aplasma treatment or a CMP (Chemical Mechanical Polishing) treatment.Besides, flattening can also be made by using a treatment of rubbingwith a high molecular material (for example, polyvinyl alcohol polymer)or the like.

Next, contact holes are formed in the interlayer insulating film, andwiring lines 260 to 266 are formed. At this time, the wiring line 266 isformed to be connected with the pixel electrode 259. In this embodiment,this wiring line is made as the laminate film of three-layer structurein which a titanium film having a thickness of 150 nm, an aluminum filmcontaining titanium and having a thickness of 300 nm, and a titaniumfilm having a thickness of 100 nm are continuously formed from the lowerlayer side by a sputtering method.

At this time, the wiring lines 260 and 262 function as source wiringlines of a CMOS circuit, and the wiring line 261 functions as a drainwiring line. The wiring line 263 is a source wiring line of a switchingtransistor, and the wiring line 264 is a drain wiring line of theswitching transistor. The wiring line 265 is a source wiring line(equivalent to a current supply line) of a current control transistor,and the wiring line 266 is a drain wiring line of the current controltransistor and is connected with the pixel electrode 259.

Next, as shown in FIG. 4B, an insulating film (hereinafter referred toas a bank) 267 having an opening portion on the pixel electrode isformed. The bank 267 may be formed by patterning an insulating filmhaving a thickness of 100 to 400 nm and containing silicon or an organicresin film. This bank 267 is formed to fill a portion between a pixeland a pixel (between a pixel electrode and a pixel electrode). Besides,it also has an object to prevent a subsequently formed organic EL filmsuch as a light emitting layer from being brought into direct contactwith the end portion of the pixel electrode 259.

Incidentally, since the bank 267 is an insulating film, attention mustbe paid to electrostatic damage of a device at the time of filmformation. When carbon particles or metal particles are added into theinsulating film, which becomes a material of the bank, to lower itsresistivity, the generation of static electricity at the time of filmformation can be suppressed. In that case, it is appropriate that theamount of addition of carbon particles or metal particles is adjusted sothat the resistivity of the insulating film, which becomes a material ofthe bank 267, becomes 1×10⁶ to 1×10¹² Ωm (preferably, 1×10⁸ to 1×10¹⁰Ωm).

When the carbon particles or the metal particles are added to the bank267, optical absorption is raised and transmissivity is lowered. Thatis, since light from the outside of the light emitting device isabsorbed, it is possible to avoid such a disadvantage that an outsidescene is reflected in the cathode surface of the EL element.

Next, an EL layer 268 is formed by an evaporation method. Incidentally,in this embodiment, a laminate layer of a hole injecting layer and alight emitting layer is called an EL layer. That is, a laminate layer ofa combination of a hole injecting layer, a hole transporting layer, ahole blocking layer, an electron transporting layer, an electroninjecting layer, or an electron blocking layer and a light emittinglayer is defined as the EL layer. In this embodiment, it is possible touse a well-known light emitting layer, hole injecting layer, holetransporting layer, hole blocking layer, electron transporting layer,electron injecting layer, or electron blocking layer.

In this embodiment, first, as the hole injecting layer, a copperphthalocyanine (CuPc) film is formed to a thickness of 20 nm, andfurther, aluminum quinolinolato complex (Alq₃) is formed to a thicknessof 80 nm as the light emitting layer. Besides, a dopant (typically,fluorescent pigment) which becomes a light emitting center may be addedto the light emitting layer by codeposition.

Next, after the EL layer 268 is formed, a cathode 269 made of aconductive film which has a small work function is formed to a thicknessof 300 nm. As the conductive film having the small work function, aconductive film containing an element belonging to group 1 or group 2 ofthe periodic table may be used. In this embodiment, a conductive filmmade of a compound of lithium and aluminum is used.

In this way, an EL element 270 including the pixel electrode (anode)259, the EL layer 268, and the cathode 269 is formed.

Note that, it is effective to provide a passivation film 271 tocompletely cover the EL element 270 after the cathode 269 is formed. Asthe passivation film 271, a single layer of an insulating film includinga carbon film, a silicon nitride film, or a silicon nitride oxide film,or a laminate layer of a combination of the insulating films is used.

At this time, it is preferable to use a film having an excellentcoverage as the passivation film, and it is effective to use a carbonfilm, especially a DLC (Diamond-Like Carbon) film. Since the DLC filmcan be formed in the temperature range of from room temperature to 100 Cor less, it can also be formed easily over the EL layer 268 having lowheat resistance. Besides, the DLC film has a high blocking effect tooxygen, and can suppress oxidation of the EL layer 268. Thus, it ispossible, to prevent such a problem that the EL layer 268 is oxidizedduring a subsequently performed sealing step.

Further, a seal member (not shown) is provided on the substrate 201 (orthe under film 202) so as to surround at least the pixel portion, and acover member 272 is bonded. As the seal member 569, an ultraviolet raycuring resin which has little degassing and resistance to the permeationof water and oxygen may be used. A space 273 may be filled with an inertgas (nitrogen gas or rare gas), a resin (ultraviolet ray curing resin orepoxy resin) or an inert liquid.

Besides, it is effective to provide a material having a moistureabsorption effect or a material having an oxidation preventing effect inthe space 273. As the cover member 272, a glass substrate, a metalsubstrate (preferably a stainless substrate), a ceramic substrate or aplastic substrate (including a plastic film) may be used. In the casewhere the plastic substrate is used, it is preferable to provide acarbon film (preferably a diamond-like carbon film) on the front surfaceand the rear surface to prevent the permeation of oxygen and water.

In this way, the light emitting device as shown in FIG. 4B is completed.Note that, it is effective that after the bank 267 is formed, the stepsup to the formation of the passivation film 271 are continuouslyperformed by using a film formation device of a multi-chamber system (oran inline system) without opening to the air. By further developing it,it is also possible to continuously perform the steps up to the bondingof the cover member 272 without opening to the air.

In this way, an n-channel transistor 601, a p-channel transistor 602, aswitching transistor (a transistor functioning as a switching elementfor transmitting an image data signal into a pixel) 603, and a currentcontrol transistor (a transistor functioning as a current controlelement for controlling electric current flowing to the EL element) 604are formed on the glass substrate 201.

At this time, the driving circuit includes, as a basic circuit, the CMOScircuit in which the n-channel transistor 601 and the p-channeltransistor 602 are complementarily combined. The pixel portion is formedof a plurality of pixels including the switching transistor 603 and thecurrent control transistor 604.

The numbers of photolithography steps needed in the manufacturing stepsup to this point is seven times, and they are smaller than that of ageneral active matrix type light emitting device. That is, themanufacturing steps of a transistor are greatly simplified, and theimprovement of yield and the reduction of manufacturing cost can berealized.

Further, as described by the use of FIG. 3A, by providing the impurityregion overlapping the first gate electrode through the gate insulatingfilm, it is possible to form the n-channel transistor having highresistance to deterioration due to the hot carrier effect. Thus, thelight emitting device having high reliability can be realized.

Further, the light emitting device of the embodiment after the seal (orencapsulation) step for protecting the EL element is performed will bedescribed with reference to FIGS. 5A and 5B. Note that, referencenumerals used in FIGS. 2 to 4 are cited as needed.

FIG. 5A is a top view showing a state where steps up to sealing of an ELelement are performed, and FIG. 5B is a cross sectional view of FIG. 5Ataken along with the line A-A′. Reference numeral 501 of a portion shownby a dotted line designates a pixel portion; 502, a source side drivingcircuit; and 503, a gate side driving circuit. Reference numeral 504designates a cover member; 505, a first seal member; and 506, a secondseal member.

Note that, reference numeral 507 designates a wiring line, fortransmitting signals inputted to the source side driving circuit 502 andthe gate side driving circuit 503, which receives a video signal and aclock signal from an FPC (Flexible Print Circuit) 508 as an externalinput terminal. Note that, although only the FPC is shown here, a printwiring board (PWB) may be attached to the FPC.

Next, a cross sectional structure will be described with reference toFIG. 5B. A pixel portion 501 and a source side driving circuit 502 areformed on a glass substrate 201, and the pixel portion 501 is formed ofa plurality of pixels including a current controlling transistor 604 anda pixel electrode 259 electrically connected to its drain. The sourceside driving circuit 502 is formed by using a CMOS circuit (see FIG. 4B)in which an n-channel transistor 601 and a p-channel transistor 602 arecombined. Note that, a polarizing plate (typically, a circularpolarizing plate) may be bonded to the glass substrate 201.

The pixel electrode 259 functions as an anode of the EL element. Banks267 are formed at both ends of the pixel electrode 259, and an EL layer268 and a cathode 269 of the EL element are formed on the pixelelectrode 259. The cathode 269 functions also as a wiring line common toall pixels, and is electrically connected to the FPC 508 through theconnection wiring line 507. Further, all elements included in the pixelportion 501 and the source side driving circuit 502 are covered with apassivation film 271.

A cover member 504 is bonded with a first seal member 505. A spacer maybe provided to secure an interval between the cover member 504 and theEL element. A space 273 is formed inside of the first seal member 505.It is desirable that the first seal member 505 is a material which wateror oxygen does not permeate. Further, it is effective to provide amaterial having a moisture absorption effect or a material having anoxidation preventing effect in the inside of the space 273.

Note that, it is appropriate that carbon films (specifically,diamond-like carbon films) 509 a and 509 b as protection films areformed to a thickness of 2 to 30 nm on the front surface and the rearsurface of the cover member 504. The carbon film like this has a role toprevent the infiltration of oxygen and water and to mechanically protectthe surface of the cover member 504.

Besides, after the cover member 504 is adhered, a second seal member 506is provided so as to cover the exposed surface of the first seal member505. The second seal member 506 can be made of the same material as thefirst seal member 505.

By encapsulating the EL element in the structure as described above, theEL element can be completely cut off from the outside, and it ispossible to prevent a material accelerating deterioration due tooxidation of the EL layer such as moisture or oxygen, from infiltratingfrom the outside. Accordingly, the light emitting device having highreliability can be obtained.

Note that, as shown in FIGS. 5A and 5B, the light emitting device inwhich the pixel portion and the driving circuit are provided on the samesubstrate and the FPC is attached, is especially called a drivingcircuit built-in light emitting device in the present specification.

The light emitting device fabricated by carrying out this embodiment canbe operated by both a digital signal and an analog signal.

Embodiment 2

In this embodiment, an example in which an active matrix type lightemitting device is fabricated by a fabricating process different fromthe embodiment 1 will be described. FIGS. 6A to 6D are used for thedescription.

First, in accordance with the fabricating process of the embodiment 1,steps up to FIG. 2C are performed. The state is shown in FIG. 6A. Inthis embodiment, a selection ratio of a first conductive film 209 and asecond conductive film 210 is made smaller than the embodiment 1, andthe second conductive film 210 is etched. In this case, in the etchingstep of FIG. 2C, it is appropriate that the flow of an oxygen gas ismade 5.0×10⁻⁶ to 8.0×10⁻⁶ m³/min.

By doing so, in the first conductive film 209, portions which are notconcealed by electrodes 212 to 216 made of the second conductive filmare slightly etched and the film thickness is decreased. In thisembodiment, an n-type impurity element (in this embodiment, phosphorus)is added in this state, and n-type impurity regions (a) 217 to 225 areformed. An addition condition may follow the step of FIG. 2C.

Next, in accordance with the etching condition of FIG. 2E of theembodiment 1, the electrodes 212 to 216 made of the second conductivefilm are etched, and second gate electrodes 601 to 605 are formed. Atthis step, in the first conductive film 209, the portions in which thefilm thickness has been decreased at the step of FIG. 6A are removed anddisappeared, and electrodes 606 to 610 made of the first conductive filmremain (FIG. 6B).

Next, in this state, the n-type impurity element is again added underthe same condition as FIG. 2E, and n-type impurity regions (b) 611 to620 are formed (FIG. 6C).

Next, under the same etching condition as FIG. 3A, the electrodes 606 to610 made of the first conductive film are etched, and first gateelectrodes 621 to 625 are formed. At this time, the n-type impurityregion (b) 611 is divided into a region 611 a not overlapping the firstgate electrode 621 and a region 611 b overlapping there through the gateinsulating film. The n-type impurity region (b) 612 is divided into aregion 612 a not overlapping the first gate electrode 621 and a region612 b overlapping there through the gate insulating film (FIG. 6D).

When subsequent steps are performed in accordance with the stepssubsequent to FIG. 3B, the active matrix type light emitting deviceshown in FIG. 4B is completed. According to this embodiment, since thedecrease of the film thickness of the gate insulating film can besuppressed, it is effective in the case where the thickness of the gateinsulating film becomes as thin as 50 to 100 nm. Note that, thisembodiment is such that the part of the fabricating steps of theembodiment 1 is changed, and the structure of the embodiment 1 can becited for the structure other than the one described in this embodiment.

Embodiment 3

In this embodiment, an example in which an active matrix type lightemitting device is fabricated by a fabricating process different fromthe embodiment 1 will be described. FIGS. 7A to 7C are used for thedescription.

First, in accordance with the fabricating steps of the embodiment 1,steps up to FIG. 2C are performed. The state is shown in FIG. 7A. Next,in accordance with the etching condition of FIG. 2E of the embodiment 1,electrodes 212 to 216 made of a second conductive film are etched, andsecond gate electrodes 701 to 705 are formed (FIG. 7B).

Next, in this state, an n-type impurity element is again added under thesame condition as FIG. 2E, and n-type impurity regions (b) 706 to 715are formed.

Next, under the same etching condition as FIG. 3A, the first conductivefilm 209 is etched, and first gate electrodes 716 to 720 are formed. Atthis time, the n-type impurity region (b) 706 is divided into a region706 a not overlapping the first gate electrode 716 and a region 706 boverlapping there through the gate insulating film. The n-type impurityregion (b) 707 is divided into a region 707 a not overlapping the firstgate electrode 716 and a region 707 b overlapping there through the gateinsulating film (FIG. 7C).

When subsequent steps are performed in accordance with the stepssubsequent to FIG. 3B, the active matrix type light emitting deviceshown in FIG. 4B is completed. According to this embodiment, since thedecrease of the film thickness of the gate insulating film can besuppressed to the utmost, it is effective in the case where thethickness of the gate insulating film becomes as thin as 50 to 100 nm.Note that, this embodiment is such that the part of the fabricatingsteps of the embodiment 1 is changed, and the structure of theembodiment 1 can be cited for the structure other than the one describedin this embodiment.

Embodiment 4

In this embodiment, an example of a manufacturing method of acrystalline semiconductor film different to that in Embodiment 1 isdescribed. FIGS. 8 and 9 are referred to in the description.

First, a glass substrate 801 is prepared, and a first silicon nitrideoxide film 802 a with a thickness of 100 nm, a second silicon nitrideoxide film 802 b with a thickness of 200 nm, and an amorphous siliconfilm 803 with a thickness of 50 nm are formed thereon. At this time, itis preferable that the concentration of nitrogen contained in the firstsilicon nitride film 802 a is made higher than the concentration ofnitrogen contained in the second silicon nitride film 802 b (FIG. 8A).

Next, nickel (Ni) is added by plasma processing to the amorphous siliconfilm 803. In the method of adding the nickel, a nickel electrode is usedto form plasma of nitrogen gas, ammonia gas, hydrogen gas or noble gas.Note that, in place of nickel, palladium, cobalt, platinum, copper,iridium, or germanium may be used. In this way an amorphous silicon film804 added with nickel is obtained (FIG. 8B).

Next, as a protecting film 805, a silicon oxide film with a thickness of50 to 150 nm is formed. Thereafter, dehydrogenation is conducted in theamorphous silicon film 804 by furnace annealing at 400 to 500° C., andthen crystallization of the amorphous silicon film 804 by furnaceannealing at 550 to 650° C. is performed. With this crystallizationprocess, the crystalline silicon film 806 is formed (FIG. 8C).

Note that, in this embodiment, the series of processes of forming thefirst silicon nitride film 802 a, forming the second silicon nitridefilm 802 b, forming the amorphous silicon film 803, plasma processing ofnickel, and forming of the protecting film 805 are continuouslyperformed in the same device. For the processes, a device with a multichamber method having the respective film formation chambers and aplasma processing chamber (a cluster tool method) may be used.

Next, a p-type impurity element (in this embodiment, boron) may be addedinto the crystalline silicon film 806 from above the protecting film805. The concentration of boron added at this time may be 1×10¹⁵ to1×10¹⁸ atoms/cm³. In this way a crystalline silicon film 807 added withboron at a concentration of 1×10¹⁵ to 1×10¹⁸ atoms/cm³ is obtained.Boron added here is an impurity element for adjusting the thresholdvoltage of the transistor.

Further, by providing the protecting film 805, a fine adjustment ofconcentration may be performed. Note that, in this embodiment, anexample of adding boron to the entire crystalline silicon film 806 isshown, but boron may be added partially by using a mask. Further, ann-type impurity element may be added, or an n-type impurity element anda p-type impurity element may be added.

Next, a protecting film 805 is removed and laser annealing is performedfor the exposed crystalline silicon film 807. As a laser, a solid-statelaser (typically, an Nd:YAG laser) or an excimer laser may be used. Bythis laser annealing, a crystalline silicon film 808 with improvedcrystallinity may be obtained.

Note that, the order of the crystallization process by furnaceannealing, the doping process of a p-type impurity element and the laserannealing process may be switched. For example, the doping process ofthe p-type impurity element may be conducted before the crystallizationprocess by furnace annealing, or after a laser annealing process.

After a crystalline silicon film 808 is obtained as described above, anactive matrix type light emitting device is manufactured according tothe processes after FIG. 2B of Embodiment 1. However, when implementingthis embodiment, metal elements such as nickel, palladium, cobalt,platinum, copper, and iridium are contained in the crystalline siliconfilm which is to be an active layer. Such a metal element may become asilicide and may become a path of current that leaks, so it ispreferably removed as much as possible.

Then, in this embodiment nickel in the crystalline silicon film isreduced by gettering nickel with phosphorus. For that reason, thetemperature of the activation process shown in FIG. 3C is set quite highat 500 to 600° C. FIG. 9 shows the above description.

When the activation process is performed in the temperature range of 500to 600° C., simultaneously nickel moves in the direction of the arrow inFIG. 9, to thereby be captured (gettered) in the region doped withphosphorus. Therefore, the concentration of nickel in the region shownby reference numerals 901 to 905 (the channel forming region oftransistors) is reduced to 1×10¹⁷ atoms/cm³ or less in measurement ofSIMS (secondary ion mass spectrometer).

The transistor manufactured according to the structure of thisembodiment has good crystallinity of the active layer (especially thechannel forming region), and shows high electric field effect mobility,and small subthreshold coefficient. Therefore a transistor with fastoperating speed may be formed.

Note that, the structure of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 3.

Embodiment 5

In this embodiment, a case of manufacturing an active matrix type lightemitting device with a manufacturing method different to that ofEmbodiment 1 is described.

In Embodiment 1, the process of forming the first inorganic insulatingfilm 256, the process of activation, the process of forming the secondinorganic insulating film 257, and the process of heat treatment at 350to 450° C. are performed in this order, but the order may be switched.

First, the process of forming the first inorganic insulating film 256,the process of forming the second inorganic insulating film 257, theprocess of activation, and the process of heat treatment at 350 to 450°C. may be performed in that order.

Further, the process of forming the first inorganic insulating film 256may be omitted., so that the process of forming the second inorganicinsulating film 257, the process of activation, and the process of heattreatment at 350 to 450° C. may be performed in that order.

Further, the process of forming the first inorganic insulating film 256may be omitted, so that the process of activation, the process offorming the second inorganic insulating film 257, and the process ofheat treatment at 350 to 450° C. may be performed in that order.

Note that, the structure of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 4.

Embodiment 6

In this embodiment, an example of combining the use of an organiccompound which emits light by a singlet exciton (singlet) (hereinafter,referred to as a singlet compound), and an organic compound which emitslight by a triplet exciton (triplet) (hereinafter, referred to as atriplet compound) as a light emitting layer is described. Note that, asinglet compound refers to a compound which emits light through only asinglet excitation, and a triplet compound refers to a compound whichemits light through a triplet excitation.

As a triplet compound, the organic compounds disclosed in the articlesbelow may be given as typical materials.

(1) T. Tsutsui, C. Adachi, S. Saito, Photochemical Processes inOrganized Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo,1991) p. 437.

(2) M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E.Thompson, S. R. Forrest, Nature 395 (1998) p. 151.

In these articles there are disclosed organic compounds shown by thefollowing formulas.

(3) M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S. R.Forrest, Appl. Phys. Lett., 75 (1999) p. 4.

(4) T. Tsutsui, M. J. Yang, M. Yahiro, K. Nakamura, T. Watanabe, T.Tsuji, Y. Fukuda, T. Wakimoto, S. Mayaguchi, Jpn. Appl. Phys., 38 (12B)(1999) L1502.

Further, the present inventors consider that not only the light emittingmaterials disclosed in the above articles, but also the light emittingmaterials shown by the following molecular formulas (specifically, ametal complex or an organic compound) may be used.

Chemical Formula 1

Chemical Formula 2

In the above molecular formulas, M is an element belonging to groups 8to 10 of the periodic table. In the above articles, platinum and iridiumare used. Further, the present inventors consider that since nickel,cobalt or palladium is cheaper than platinum or iridium, they are morepreferable in reducing the manufacturing cost of the light emittingdevice. Especially, since nickel can easily form a complex, productivityis high and therefore preferable.

The above-mentioned triplet compound has higher luminous efficiency thanthe singlet compound, and in obtaining the same light emittingbrightness, the operation voltage (a voltage necessary for an EL elementto emit light) may be decreased. This embodiment makes use of thisfeature.

FIG. 10 shows a cross sectional structure of the pixel portion of theactive matrix type light emitting device of this embodiment. In FIG. 10,reference numeral 10 shows an insulator, reference numeral 11 shows acurrent control transistor 604 of FIG. 4B, reference numeral 12 shows apixel electrode (anode), reference numeral 13 shows a bank, referencenumeral 14 shows a known hole injecting layer, reference numeral 15shows a light emitting layer which emits red color, reference numeral 16shows a light emitting layer which emits green color, reference numeral17 shows a light emitting layer which emits blue color, referencenumeral 18 shows a known electron transporting layer, and referencenumeral 19 shows a cathode.

Here in this embodiment, a triplet compound is used as a light emittinglayer 15 which emits red color, and a singlet compound is used as alight emitting layer 16 which emits green color and a light emittinglayer 17 which emits blue color. That is, an EL element using a singletcompound is an EL element which emits green color or blue color, and anEL element using the above-mentioned triplet compound is an EL elementwhich emits red color.

When a low molecular organic compound is used as a light emitting layer,at present the life of a light emitting layer which emits red color isshorter than a light emitting layer which emits other colored light.This is because the luminous efficiency is lower than that of othercolors, and in order to obtain the same light emitting brightness asother colors, the operation voltage has to be set higher and thusprogress of deterioration is fast.

However, in this embodiment since a triplet compound with high luminousefficiency is used as the light emitting layer 15 which emits red color,the same light emitting brightness as the light emitting layer 16 whichemits green color and the light emitting layer 17 which emits blue colormay be obtained while the operation voltage is made the same.Accordingly, the deterioration of the light emitting layer 15 whichemits red color does not progress significantly, and color display maybe performed without causing a problem such as color shift. Further,suppression of the operation voltage is preferable considering that themargin of the peak inverse voltage of the transistor may be set low.

Note that, in this embodiment an example of using a triplet compound asthe light emitting layer 15 which emits red color is shown, and atriplet compound may be used as the light emitting layer 16 which emitsgreen color or the light emitting layer 17 which emits blue color.

A circuit structure of the pixel portion in the case this, embodiment isimplemented is shown in FIG. 11. Note that, here the pixel (pixel (red))20 a which includes an EL element which emits red color, the pixel(pixel (green)) 20 b which includes an EL element which emits greencolor, and the pixel (pixel (blue)) 20 c which includes an EL elementwhich emits blue color are shown, and all have the same circuitstructure.

In FIG. 11A, reference numeral 21 denotes a gate wiring line, referencenumerals 22 a to 22 c denote source wiring lines (data wiring lines),and reference numerals 23 a to 23 c denote current supply wiring lines.The current supply wiring lines 23 a to 23 c are wiring lines fordetermining the operation voltage of the EL element, and the samevoltage is applied to any of the pixel 20 a which emits red color, thepixel 20 b which emits green color and the pixel 20 c which emits bluecolor. Therefore, the line width (thickness) of the wiring lines may allhave the same design.

Further, reference numerals 24 a to 24 c denote switching transistors,and here are formed of n-channel transistors. Note that, a structurehaving two channel forming regions in between the source region and thedrain region is illustrated here, but a structure with two or more, orone channel forming region may be used.

Further, symbols 25 a to 25 c are current control transistors, and agate is connected to any of the switching transistors 24 a to 24 c, asource is connected to any of the current supplying lines 23 a to 23 c,and a drain is connected to any of EL elements 26 a to 26 c. Note that,symbols 27 a to 27 c are capacitors, which hold a voltage to be appliedto the gate of the respective current supply lines 25 a to 25 c.However, the capacitors 27 a to 27 c may be omitted.

Note that, FIG. 11A shows an example where switching transistors 24 a to24 c formed of n-channel transistors and current control transistors 25a to 25 c formed of p-channel transistors are provided. However, asshown in FIG. 11B, switching transistors 28 a to 28 c formed ofp-channel transistors and current control transistors 29 a to 29 cformed of n-channel transistors may be provided in the pixel (red) 30 a,the pixel (green) 30 b and the pixel (blue) 30 c, respectively.

Further, in FIGS. 11A and 11B, an example of providing two transistorsin one pixel is shown, but the number of transistors may be two or more(typically 3 to 6). In such a case, the n-channel transistor and thep-channel transistor may be provided by combining them in any way.

In this embodiment, an EL element 26 a is an EL element which emits redcolor, and uses a triplet compound as the light emitting layer. Further,an EL element 26 b is an EL element which emits green color, and an ELelement 26 c is an EL element which emits blue color, and both use asinglet compound as the light emitting layer.

In this way, by using the triplet compound and the singlet compoundproperly, the operation voltage of the EL elements 26 a to 26 c may allbe made the same (10V or less, preferably 3 to 10 V). Accordingly, sincethe power source necessary for a light emitting device may be made thesame, at for example 3V or 5V, there is an advantage that the circuitdesign may be easily made.

Note that, the structures of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 5.

Embodiment 7

In this embodiment, a case where the pixel portion and the drivercircuit are all formed by the n-channel transistor is described. Notethat, the manufacturing process of the n-channel transistor is inaccordance with Embodiment 1, therefore a description thereof isomitted.

A cross sectional structure of the light emitting device of thisembodiment is shown in FIG. 12. Note that, the basic structures are thesame as the cross sectional structure shown in FIG. 4B of Embodiment 1,so only the differences are described here.

In this embodiment, an n-channel transistors 1201 is provided in placeof a p-channel transistor 602, and a current control transistor 1202formed of an n-channel transistor is provided in place of a currentcontrol transistor 604.

Further, a wiring line 266 connected to the drain of the current controltransistor 1202 functions as a cathode of an EL element, and an EL layer1203, an anode 1204 formed of an oxide conductive film, and apassivation film 1205 are formed thereon. At this time, it is preferablethat the wiring line 266 is formed of a metal film containing an elementbelonging to group 1 or 2 of the periodic table, or at least the surfacecontacting the EL layer 1203 is formed of a metal film containing anelement belonging to group 1 or 2 of the periodic table.

Further, the n-channel transistor used in this embodiment may be allenhancement type transistors, or may be depression type transistors. Ofcourse, it is possible to make both and combine them for use.

Here, the circuit structure of a pixel is shown in FIG. 13. Note that,for the portion where the same symbols as FIG. 11 is used, thedescription of FIG. 11 may be referred to.

As shown in FIG. 13, the switching transistors 24 a to 24 c provided inthe pixel (red) 35 a, the pixel (green) 35 b, and the pixel (blue) 35 c,respectively, and the current control transistors 35 a to 35 c are allformed of n-channel transistors.

According to the structure of this embodiment, in the manufacturingprocess of the light emitting device of Embodiment 1, since thephotolithography process for forming a p-channel transistor and thephotolithography process for forming a pixel electrode (anode) may beomitted, it is possible to further simplify the manufacturing process.

Note that, the structure of this embodiment may be implemented bycombining any of the structures of Embodiments 1 to 6.

Embodiment 8

In this embodiment, a case where the pixel portion and the drivingcircuit are all formed by a p-channel transistor is described. A crosssectional structure of a light emitting device of this embodiment isshown in FIG. 14. Note that, a portion with the same symbol as in FIG.4B of Embodiment 1 may refer to the description of Embodiment 1.

In this embodiment, the driving circuit is formed of a PMOS circuitformed of a p-channel transistor 1401 and a p-channel transistor 1402,and the pixel portion has a switching transistor 1403 formed of ap-channel transistor and a current control transistor 1404 formed of ap-channel transistor. Note that, the active layer of the p-channeltransistor 1401 includes the source region 41, the drain region 42, theLDD regions 43 a and 43 b and the channel forming region 44. Thestructure of the active layer is the same as in the p-channel transistor1402, the switching transistor 1403 and the current control transistor1404.

Here, the manufacturing process of the p-channel transistor of thisembodiment is described by referring to FIG. 15, First, the processuntil FIG. 2B is described in accordance with the manufacturing processof Embodiment 1.

Next, electrodes 212 to 216 which are formed of a second conductive filmare formed using resists 211 a to 211 e. Then, the resists 211 a to 211e and the electrodes 212 to 216 formed of the second conductive film areused as masks and elements belonging to group 13 of the periodic table(in this embodiment, boron) are added to a semiconductor film, therebyforming regions (hereinafter, referred to as p-type impurity region (a))301 to 309 containing boron at a concentration of 1×10²⁰ to 1×10²¹atoms/cm³ (FIG. 15A).

Next, the electrodes 212 to 216 formed of the second conductive film areetched using the resists 211 a to 211 e under the same etchingconditions as in FIG. 1D, to thereby form the second gate electrodes 310to 314 (FIG. 15B).

Next, the first conductive film 209 is etched under the same etchingconditions as in FIG. IC, with the resists 211 a to 211 e and the secondgate electrodes 310 to 314 as masks, to thereby form first gateelectrodes 315 to 319.

Then, the element belonging to croup 13 of the periodic table (in thisembodiment, boron) is doped into the semiconductor film, with theresists 211 a to 211 e and the second gate electrodes 310 to 314 asmasks, to thereby form regions (hereinafter, referred to as a p-typeimpurity region (b)) 320 to 329 containing boron at a concentration of1×10¹⁶ to 1×10¹⁹ atoms/cm³ a (typically, 1×10¹⁷ to 1×10¹⁸ atoms/cm³)(FIG. 15C).

The processes thereafter are in accordance with the processes after FIG.3C of Embodiment 1. With the above processes, the light emitting deviceof the structure shown in FIG. 14 can be formed.

Note that, the p-channel transistors used in this embodiment may all beenhancement type transistors or may all be depletion type transistors.Of course, both may be formed and combined to be used.

The circuit structure of the pixel is shown in FIG. 16. Note that theportion with the same symbols as in FIG. 11 may refer to the descriptionof FIG. 11.

As shown in FIG. 16, the switching transistors 51 a to 51 c and thecurrent control transistors 52 a to 52 c provided respectively in apixel (red) 50 a, a pixel (green) 50 b, and a pixel (blue) 50 c are allformed of p-channel transistors.

According to the structure of this embodiment, since the firstphotolithography process in the manufacturing process of the lightemitting device of Embodiment 1 may be omitted, the manufacturingprocess may be simplified more than in Embodiment 1.

Note that, the structure of this embodiment may be implemented incombination with any of the structures of Embodiments 1 to 6.

Embodiment 9

The active matrix type light emitting device of this invention may use,as a semiconductor element, a MOS (Metal Oxide Semiconductor)transistor. In such a case, a MOS transistor formed with a known methodmay be used as the semiconductor substrate (typically, a silicon wafer).

Note that, the structure of this embodiment may be implemented incombination with the structures of Embodiments 1 to 3, and 5 to 8.

Embodiment 10

In Embodiment 1, a driving circuit built-in light emitting device shownin FIG. 5 is an example of a pixel portion and a driving circuitintegrally formed on the same insulator, but a driving circuit may alsobe provided with an externally mounted IC (integrated circuit). In sucha case, the structure is as shown in FIG. 17A.

In the module shown in FIG. 17A, an FPC 63 is mounted on an activematrix substrate 60 (including a pixel portion 61, wiring 62 a and 62b), and a printed wiring board 64 is mounted through the FPC 63. Here,the functional block diagram of the printed wiring board 64 is shown inFIG. 17B.

As shown in FIG. 17B, the printed wiring board 64 is provided with atleast I/O ports (also referred to as an input or output portion) 65 and68, and an IC which functions as a source side driver circuit 66 and agate side driver circuit 67.

In this way, a module with a structure where an active matrix substrateformed with a pixel portion on the substrate surface is mounted with anFPC, and a structure where a printed wiring board having a function as adriving circuit through the FPC is referred to as a light emittingmodule having an external driving circuit particularly throughout thisspecification.

Further, in the module shown in FIG. 18A, a driving circuit built-inlight a emitting device 70 (including a pixel portion 71, a source sidedriving circuit 72, a gate side driving circuit 73, wiring lines 72 aand 73 a) is mounted with an FPC 74, and a printed wiring board 75 ismounted through the FPC 74. The functional block diagram of a printedwiring board 75 is shown in FIG. 18B.

As shown in FIG. 18B, the printed wiring board 75 is provided with atleast an I/O port 76 and 79, and an IC which functions as a controlportion 77. Note that here a memory portion 78 is provided, but it isnot always necessary. Further, the control portion 77 is a portionhaving a function for controlling the driving circuit, correctingpicture data, and the like.

A module with a structure where a driving circuit built-in lightemitting device formed with a pixel portion and a driving circuit on theboard surface is mounted with a printed wiring board having a functionas a controller in this way, is referred to as a light emitting modulewith an external controller particularly in this specification.

Embodiment 11

The light-emitting device (including the module at the state of which isshown in Embodiment 10) formed by implementing this invention may beused as a display portion of various electrical appliances. Aselectrical appliances of this invention, there are such as an imageplayback device with a video camera, a digital camera, a goggle typedisplay (head mounted display), a car navigation system, an audioapparatus, a note type personal computer, a game apparatus, a portableinformation terminal (such as a mobile computer, a portable telephone, aportable game apparatus or an electronic book), and an imagereproduction D device providing a recording medium. Specific examples ofthe electronic equipment are shown in FIGS. 19 and 20.

FIG. 19A shows an EL display and includes a casing 2001, a supportingbase 2002 and a display portion 2003. The light-emitting device of thisinvention may be used for the display portion 2003. When using thelight-emitting device having the EL element in the display portion 2003,since the EL element is a self-light emitting type backlight is notnecessary and the display portion may be made thin.

FIG. 19B shows a video camera, which contains a main body 2101, adisplay portion 2102, a sound input portion 2103, operation switches2104, a battery 2105, and an image receiving portion 2106. Thelight-emitting device of this invention can be applied to the displayportion 2102.

FIG. 19C shows a digital camera, which contains a main body 2201, adisplay portion 2202, an eye contact portion 2203, and operationswitches 2204. The light emitting-device and the liquid crystal displaydevice of this invention can be applied to the display portion 2202.

FIG. 19D shows an image playback device equipped with a recording medium(specifically, a DVD playback device), which contains a main body 2301,a recording medium (such as a CD, LD or DVD) 2302, operation switches2303, a display portion (a) 2304, a display portion (b) 2305 and thelike. The display portion (a) is mainly used for displaying imageinformation. The display portion (b) 2305 is mainly used for displayingcharacter information. The light-emitting device of this invention canbe applied to the display portion (a) and the display portion (b). Notethat, the image playback device equipped with the recording mediumincludes devices such as CD playback device, and game machines.

FIG. 19E shows a portable (mobile) computer, which contains a main body2401, a display portion 2402, an image receiving portion 2403, operationswitches 2404 and a memory slot 2405. The light-emitting device of thisinvention can be applied to the display portion 2402. This portablecomputer may record information to a recording medium that hasaccumulated flash memory or involatile memory, and playback suchinformation.

FIG. 19F shows a personal computer, which contains a main body 2501, acasing 2502, a display portion 2503, and a keyboard 2504. Thelight-emitting device of this invention can be applied to the displayportion 2503.

The above electronic appliances more often display information sentthrough electron communication circuits such as the internet or the CATS(cable television), and especially image information display isincreasing. When using the light-emitting device having the EL elementin the display portion, since the response speed of the EL element isextremely fast, it becomes possible to display pictures without delay.

Further, since the light emitting portion of the light-emitting deviceconsumes power, it is preferable to display information so that thelight emitting portion is as small as possible. Therefore, when usingthe light-emitting device in the portable information terminal,especially in the display portion where character information is mainlyshown in a portable phone or an audio apparatus, it is preferable todrive so that the character information is formed of a light emittingportion with the non-light emitting portion as a background.

Here, FIG. 20A shows a portable telephone, and reference numeral 2601shows a portion (operation portion) which performs key operation, andreference numeral 2602 shows a portion which performs informationdisplay (information display portion), and the operation portion 2601and the information display portion 2602 are connected by the connectingportion 2603. Further, the operation portion 2601 is provided with asound input portion 2604, operation switches 2605, and the informationdisplay potion 2602 is provided with a sound output portion 2606, adisplay portion 2607.

The light-emitting device of this invention may be used as the displayportion 2607. Note that, when using the light-emitting device to thedisplay portion 2607, the consumption power of the portable telephonemay be suppressed by displaying white letters in the background of theblack color.

In the case of the portable telephone shown in FIG. 20A, thelight-emitting device used in the display portion 2604 is incorporatedwith a sensor by a CMOS circuit(a CMOS sensor), and may be used as anauthentication system terminal for authenticating the user by readingthe fingerprints or the hand of the user. Further, light emission may beperformed by taking into consideration the brightness (illumination) ofoutside and making information display at a contrast that is alreadyset.

Further, the low power consumption may be attained by decreasing thebrightness when using the operating switch 2605 and increasing thebrightness when the use of the operation switch is finished. Further,the brightness of the display portion 2604 is increased when a call isreceived, and low power consumption is attained by decreasing thebrightness during a telephone conversation. Further, when using thetelephone continuously, by making it have a function so that display isturned off by time control unless it is reset, low power consumption isrealized. It should be noted that this control may be operated by hand.

Further, FIG. 20B shows an audio, which contains a casing 2701, adisplay portion 2702, and operation switches 2703 and 2704. Thelight-emitting device of this invention can be applied to the displayportion 2702. Further, in this embodiment, a car mounted audio (caraudio) is shown, but it may be used in a fixed type audio (audiocomponent). Note that, when using a light-emitting device in the displayportion 2704, by displaying white characters in a black background,power consumption may be suppressed.

Further, electrical equipments shown above are incorporated with a lightsensor in the light-emitting device which are used in the displayportion, and it is possible to provide means to detect the brightness ofthe environment of use. When using the light-emitting device in thedisplay portion, it is may have a function that modulates thelight-emission brightness according to the brightness of the environmentof use.

Specifically, this is implemented by providing an image sensor (surfaceshape, linear or a dotted sensor) formed by a CMOS circuit on thelight-emitting device using the display portion, and providing a CCD(charge coupled device) on the main body or the casing. The user mayrecognize the image or the character information without trouble if abrightness of a contrast ratio of 100 to 150 may be maintained ascompared to the brightness of the environment of use. Namely, in thecase the environment of use is dark, it is possible to suppress theconsumption power by suppressing the brightness of the image.

As in the above, the applicable range of this invention is extremelywide, and may be used for various electrical equipment. Further, theelectrical equipment of this embodiment may use the light-emittingdevice and the module containing any of the structures of Embodiments 1to 10.

By carrying out the present invention, a light emitting device can bemanufactured at a high yield and a low cost, and an inexpensive lightemitting device can be provided. Besides, it becomes possible to providean inexpensive electric instrument by using the inexpensive lightemitting device as a display portion.

1. A method of fabricating a light emitting device, comprising the stepsof: forming a semiconductor film over an insulating surface; forming agate insulating film covering the semiconductor film; forming a firstconductive film over the gate insulating film; forming a secondconductive film over the first conductive film; etching the secondconductive film to form a first electrode by ICP etching so that sidesurfaces of the first electrode are tapered; and etching the firstconductive film to form a second electrode by ICP etching so that sidesurfaces of the second electrode are tapered.
 2. A method of fabricatinga light emitting device according to claim 1, wherein the firstconductive film is formed of a tantalum nitride film, and wherein thesecond conductive film is formed of a tungsten film.
 3. A method offabricating a light emitting device according to claim 1, wherein thefirst conductive film is formed of a tungsten film, and wherein thesecond conductive film is formed of an aluminum alloy film.
 4. A methodof fabricating a light emitting device according to claim 1, wherein thefirst conductive film is formed of a titanium nitride film, and whereinthe second conductive film is formed of a tungsten film.
 5. A method offabricating a light emitting device according to claim 1, wherein awidth of the first electrode is narrower than a width of the secondelectrode.
 6. A method of fabricating a light emitting device accordingto claim 1, wherein a mixture gas of a carbon tetrafluoride gas and achlorine gas is used in the step of etching the first conductive film.7. A method of fabricating a light emitting device according to claim 1,wherein a mixture gas of a carbon tetrafluoride gas, a chlorine gas andan oxygen gas is used in the step of etching the second conductive film.8. A method of fabricating a light emitting device according to claim 1,wherein the passivation film is a silicon nitride film or a siliconnitride oxide film.
 9. A method of fabricating a light emitting deviceaccording to claim 1, wherein the interlayer insulating film is aninorganic insulating film, an organic insulating film, or a laminatefilm of those.
 10. A method of fabricating a light emitting deviceaccording to claim 1, wherein the impurity element is an n-type impurityelement or a p-type impurity element.
 11. A method of fabricating alight emitting device according to claim 1, wherein the light emittingdevice is incorporated into an electronic appliance selected from thegroup consisting of an EL display, a camera, a personal computer, agoggle type display, and a navigation system.
 12. A method offabricating a light emitting device according to claim 1, wherein amixture gas used in the step of etching the first conductive film isdifferent from a mixture gas used in the step of etching the secondconductive film.
 13. A method of fabricating a light emitting devicecomprising the steps of: forming a semiconductor film over an insulatingsurface; forming a gate insulating film covering the semiconductor film;forming a first conductive film over the gate insulating film; forming asecond conductive film over the first conductive film; etching thesecond conductive film to form a first electrode by ICP etching so thatside surfaces of the first electrode are tapered; etching the firstconductive film to form a second electrode by ICP etching so that sidesurfaces of the second electrode are tapered; forming a passivation filmover the second electrode; and forming an interlayer insulating filmover the passivation film.
 14. A method of fabricating a light emittingdevice according to claim 13, wherein the first conductive film isformed of a tantalum nitride film, and wherein the second conductivefilm is formed of a tungsten film.
 15. A method of fabricating a lightemitting device according to claim 13, wherein the first conductive filmis formed of a tungsten film, and wherein the second conductive film isformed of an aluminum alloy film.
 16. A method of fabricating a lightemitting device according to claim 13, wherein the first conductive filmis formed of a titanium nitride film, and wherein the second conductivefilm is formed of a tungsten film.
 17. A method of fabricating a lightemitting device according to claim 13, wherein a width of the firstelectrode is narrower than a width of the second electrode.
 18. A methodof fabricating a light emitting device according to claim 13, wherein amixture gas of a carbon tetrafluoride gas and a chlorine gas is used inthe step of etching the first conductive film.
 19. A method offabricating a light emitting device according to claim 13, wherein amixture gas of a carbon tetrafluoride gas, a chlorine gas and an oxygengas is used in the step of etching the second conductive film.
 20. Amethod of fabricating a light emitting device according to claim 13,wherein the passivation film is a silicon nitride film or a siliconnitride oxide film.
 21. A method of fabricating a light emitting deviceaccording to claim 13, wherein the interlayer insulating film is aninorganic insulating film, an organic insulating film, or a laminatefilm of those.
 22. A method of fabricating a light emitting deviceaccording to claim 13, wherein the impurity element is an n-typeimpurity element or a p-type impurity element.
 23. A method offabricating a light emitting device according to claim 13, wherein thelight emitting device is incorporated into an electronic applianceselected from the group consisting of an EL display, a camera, apersonal computer, a goggle type display, and a navigation system.
 24. Amethod of fabricating a light emitting device according to claim 13,wherein a mixture gas used in the step of etching the first conductivefilm is different from a mixture gas used in the step of etching thesecond conductive film.
 25. A method of fabricating a light emittingdevice comprising the steps of: forming a semiconductor film over aninsulating surface; forming a gate insulating film covering thesemiconductor film; forming a first conductive film over the gateinsulating film; forming a second conductive film over the firstconductive film; etching the second conductive film to form a firstelectrode by ICP etching so that side surfaces of the first electrodeare tapered; adding an impurity element to the semiconductor filmthrough the first conductive film; and etching the first conductive filmto form a second electrode by ICP etching so that side surfaces of thesecond electrode are tapered.
 26. A method of fabricating a lightemitting device according to claim 25, wherein the first conductive filmis formed of a tantalum nitride film, and wherein the second conductivefilm is formed of a tungsten film.
 27. A method of fabricating a lightemitting device according to claim 25, wherein the first conductive filmis formed of a tungsten film, and wherein the second conductive film isformed of an aluminum alloy film.
 28. A method of fabricating a lightemitting device according to claim 25, wherein the first conductive filmis formed of a titanium nitride film, and wherein the second conductivefilm is formed of a tungsten film.
 29. A method of fabricating a lightemitting device according to claim 25, wherein a width of the firstelectrode is narrower than a width of the second electrode.
 30. A methodof fabricating alight emitting device according to claim 25, wherein amixture gas of a carbon tetrafluoride gas and a chlorine gas is used inthe step of etching the first conductive film.
 31. A method offabricating a light emitting device according to claim 25, wherein amixture gas of a carbon tetrafluoride gas, a chlorine gas and an oxygengas is used in the step of etching the second conductive film.
 32. Amethod of fabricating a light emitting device according to claim 25,wherein the passivation film is a silicon nitride film or a siliconnitride oxide film.
 33. A method of fabricating a light emitting deviceaccording to claim 25, wherein the interlayer insulating film is aninorganic insulating film, an organic insulating film, or a laminatefilm of those.
 34. A method of fabricating a light emitting deviceaccording to claim 25, wherein the impurity element is an n-typeimpurity element or a p-type impurity element.
 35. A method offabricating a light emitting device according to claim 25, wherein thelight emitting device is incorporated into an electronic applianceselected from the group consisting of an EL display, a camera, apersonal computer, a goggle type display, and a navigation system.
 36. Amethod of fabricating a light emitting device according to claim 25,wherein a mixture gas used in the step of etching the first conductivefilm is different from a mixture gas used in the step of etching thesecond conductive film.